The present invention relates to combining and/or splitting high power, high frequency RF signals and, more particularly, to a device for dynamically combining or splitting high power, high frequency RF signals.
Wireless communication infrastructures include high power RF signal systems in which it is desirable to combine signals of the various input lines having coherent sources with little or no insertion loss, regardless of how many of the inputs are selected at any one time. For example, a common cellular base station includes systems that utilize from one to four amplifiers. Usually it is a requirement that all amplifier outputs be equal in magnitude and have the same phase. The system must support any combination of one to four in any possible combination of amplifier positions. In addition, the system must be able to reconfigure to maintain optimum performance when one or more amplifiers fail. In typical wireless communication systems, the system would preferably act as a piece of 50 Ohm transmission line, or a two way combiner, or a three way combiner, or a four way combiner with the inputs being able to connect to any available combination of amplifier locations.
There are known to those skilled in the art various methods of achieving some of these demands. For instance, U.S. Pat. No. 4,315,222 to Saleh describes an N-way non-hybrid power combiner arrangement for microwave amplifiers. The Saleh patent describes the use of sensing means that are coupled in one-to-one relationships with the individual amplifiers to monitor amplifier performance and/or failure. The method utilizes shorting devices that are disposed adjacent to the outputs of the individual amplifiers and are coupled to the associated sensing means in a one-to-one relationship. Upon identifying amplifier failure, the sensing means coupled to that particular amplifier activates either its associated short-circuiting or open-circuiting device, which in turn uncouples the failed amplifier and the transmission line associated therewith.
An additional method of achieving some of the demands of high frequency wireless communication systems is described in U.S. Pat. No. 6,252,871 to Posner et al. which describes an apparatus for either combining a plurality of high frequency RF signal inputs or splitting a single RF frequency input into a plurality of RF signal outputs that employs a switchable combining/splitting section and a switchable matching section. The switchable combining/splitting section operates to either combine the RF signal inputs to a common summed output or to take a matched input and to split it into a plurality of elements. The matching section operates to switchably match the impedance presented by the combining/splitting section to achieve a minimum or zero insertion loss through the apparatus.
Although the prior art contains some methods to overcome the problems associated with wireless communication infrastructure as described above, there is still a need for a simple and relatively inexpensive system that allows dynamically combining amplifiers in wireless communication systems.
One object of the claimed invention is to provide adjustable impedance with a fixed length quarter-wave transmission line or equivalent transformer.
It is another object of this invention to provide a method of combining transformer impedances and replacing it with a single transformer.
It is yet another object of this invention to provide increasing performance by reducing the complexity of amplifier circuitry.
It is a further object of this invention to use coupled line circuitry to create switchable impedance in order to increase the performance of a wireless communication system.
These and other goals are accomplished by providing a circuit for dynamically combining/splitting power amplifier outputs that comprises four power input ports. The input ports are joined by a 360 degree transmission line having three switches spaced 90 degrees apart. Two coupled line circuits are connected to the transmission line. The coupled line circuits are placed in parallel and each of the coupled line circuits selectively provides either 50 Ohms or 70.7 Ohms impedance.